I have been a Minimed pumper for the past 12 years. This problem suddenly started about 5 months ago. The reservior would be bubble free on fill - after 12 hrs bubbles would appear and gradually grow to 1/3 volume at which point I would have to replace the reservior and infusion set.

I complained to Minimed and was told that I was doing something wrong. The local Minimed Rep monitored me filling reserviors and confirmed that I was following correct procedures. This problem is not confined to a single resevior or insulin batch.

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As with Natalie, I got my first pump in 1999 and was trained to slowly move the plunger up and down in the reservoir first (spreading lubricant). After doing this for 4 yrs. with the first pump, I have been doing it ever since. Never had any problems with larger bubbles that I know of, and could alway find another reason for a sudden spike in BG that happens occasionally. Also, as with Scott, I always inject equal air into a vial of insulin before withdrawing it into the reservoir.r

How old is your insulin vial? I always find that I get fewer bubbles when starting a new vial. It has to do with the air-pressure inside of there.

When you go to fill the reservoir, you should first inject a certain amount of air into the vial, then draw out an equal amount of insulin. It's the same way I did it with syringes way back in the day... this makes sure the air takes the place of the insulin you're pulling out, and the inside of the vial isn't under constant pressure.

I find that, inevitably, with the crude unit-markings on the reservoir and the constant pushing of air-bubbles back out of the reservoir (and the occasional air leakage at the O-rings), I always push more air into the vial than insulin I end up pulling out. I push in air to just shy of the the 1.8 mark (180 units), and by the time I'm done trying to push air bubbles out of the reservoir and back into the vial, I'm at 1.4. That's 40 extra units (of air) in the vial that has nowhere to go.

This ends up putting positive pressure in the vial, and the air (and insulin) end up compressed in order for it all to fit in there.

When it's moved from one place to another (i.e. a reservoir, where one end - the plunger - is moveable) the contents expand to their natural volume and might even push the plunger out ever-so-slightly, causing the tiny air bubbles to get larger.

It's just a theory, and without some scientific equipment (which I don't have), there's no way to really know for sure. But if this happens more with used than new vials, it's likely the culprit.

Try this, especially if it's an older vial: hold the vial right-side up, and attach the reservoir. Pull out 40 units of air (this number is a guess). Take the reservoir and the blue cap off of the vial and use the plunger to release the air into the room. This will lower the pressure inside the vial, and it might help.

If you feel the plunger getting "pulled back" into the vial, that means there's negative pressure/not enough air in there. If, when you try to push air into it, the plunger wants to pop back out on its own, there's positive pressure/too much air. You want to be somewhere in the middle.

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